US president Barack Obama has said the US must and will take action against Russia over hacking during the presidential election.
Mr Obama told NPR News that America would respond at a "time and place of our choosing", some of which might be publicised and some not.
The president said he had spoken directly to Vladimir Putin about his feelings over the hacking.
Whenever a foreign government tried to interfere in US elections, the nation must take action - "and we will", Mr Obama saidq.
"Some of it may be explicit and publicised, some of it may not be. But Mr Putin is well aware of my feelings about this, because I spoke to him directly about it."
On Thursday the Obama administration suggested President Putin personally authorised the hacking of Democratic officials' email accounts in the run-up to the election and said it was "fact" that such actions helped Donald Trump's campaign.
And the White House also attacked president-elect Trump himself, saying he must have known of Russia's interference.
No proof was offered for any of the accusations, the latest to unsettle America's uneasy transition from eight years under Democrat Mr Obama to a new Republican administration led by billionaire property mogul Mr Trump.
The claims of Russian meddling in the election also have heightened already debilitating tensions between Washington and Moscow over Syria, Ukraine and a host of other disagreements.
"Only Russia's senior-most officials could have authorised these activities," White House spokesman Josh Earnest said, repeating the words from an October US intelligence assessment.
Mr Obama's deputy national security adviser Ben Rhodes joined the dots further, saying it was Mr Putin who was responsible for the Russian government's actions.
"I don't think things happen in the Russian government of this consequence without Vladimir Putin knowing about it," he said.
The explosive accusation paints Mr Putin, the leader of perhaps the nation's greatest geopolitical foe, as having directly undermined US democracy.
US officials have not argued, however, that Mr Trump would have been defeated by Hillary Clinton on November 8 if not for Russia's assistance, nor has there has been any indication of tampering with the vote-counting.
The Kremlin flatly rejected the claim of Mr Putin's involvement, with Putin spokesman Dmitry Peskov dismissing it as "laughable nonsense".
The dispute over Russia's role is fuelling an increasingly public spat between Mr Obama's White House and Mr Trump's team that is threatening to spoil the delicate truce that the pair have forged since election day.
Although the president and president-elect have avoided criticising each other publicly since Mr Trump's win, their aides have been more openly antagonistic.
Kellyanne Conway, Mr Trump's senior transition adviser, said it was "breathtaking" and irresponsible that the White House had suggested Mr Trump knew Russia was interfering to help his campaign.
Mr Earnest said Mr Trump, who has dismissed the CIA's assessment of Russian interference, should spend less time attacking the intelligence community and more time supporting the investigation that Mr Obama has ordered.
Mr Earnest said it was "obvious" Mr Trump knew what Russia was doing during the campaign, pointing out that Mr Trump had encouraged Moscow during a news conference to find Mrs Clinton's missing emails. Mr Trump has said he was joking.
"I don't think anybody at the White House thinks it's funny that an adversary of the United States engaged in malicious cyber activity to destabilise our democracy," Mr Earnest said.
"That's not a joke."
US intelligence officials have linked the hacking to Russia's intelligence agency and its military intelligence division.
Moscow has denied all accusations that it orchestrated the hacking of email accounts of Democratic Party officials and Mrs Clinton's campaign chief John Podesta, then leaked them to anti-secrecy website WikiLeaks.
Mr Trump and his supporters insist the Democrats' outrage about Russia is really an attempt to undermine the validity of his election victory.
Congressman Peter King, a Trump ally and New York Republican, called it "disgraceful" as he spoke to reporters amassed in Trump Tower after meeting the president-elect.
"Right now, certain elements of the media, certain elements of the intelligence community and certain politicians are really doing the work of the Russians," he said.
But Democrats pounced on the latest suggestions of Mr Putin being connected to the daily drip of emails during the presidential race from some of Mrs Clinton's closest advisers.
Mr Putin was "clearly involved," said outgoing Senate minority leader Harry Reid.
"Having been the former head of the KGB, does that surprise you?" he said.
"And does it surprise anybody today when he denied it?"
US secretary of state John Kerry defended Mr Obama's handling of the issue during the heat of the presidential campaign - a stance now criticised by some Democrats as too weak - but said he would not comment on whether Mr Putin was involved.
"People need to remember that the president issued a warning," he said.
"But he had to be obviously sensitive to not being viewed as interfering on behalf of a candidate or against a candidate or in a way that promoted unrealistic assessments about what was happening."
